A gas turbine group comprises an air compressor, a combustion circuit and an expansion turbine coupled to the compressor for driving this latter. The expansion work performed by the turbine being greater than the work of compression of the compressor, there results an energy balance used to drive a machine such as an alternator. The work delivered by the turbine depends in large part on the quantity of fumes generated during combustion and increases with this latter within limits compatible with the aerodynamic characteristics, also called "the hydraulic", of the turbine. 0n the other hand, the energy consumed by the compressor depends on the mass of flow rate of compressed air within the pumping limits of the compressor.
A gas turbine group represents a considerable investment which is not optimally used unless the compressor and the turbine each operate within optimum conditions. This optimum condition is rarely achieved insofar as in general one of the two elements is at its optimum capacity while the other is not, which is called the disequilibrium between the two elements, the most frequent case being that in which the turbine is, aerodynamically speaking, under-dimensioned relative to the compressor whose limits are more rapidly reached. Such disequilibrium can arise among other things from the fuel used or the climatic conditions of the utilization site. Thus, for the same thermal energy released, the flow rate of the fuels will vary considerably according to the gaseous fuels. The less is the lower calorific power (LCP) of the gas, the greater is the flow rate of fumes generated. For example, the combustion of a blast furnace gas will produce, for identical thermal energy, a greater flow rate of fumes than for natural gas, this latter having on the other hand, according to its origin, variable LCPs. With a large volume of fumes, the pressure at the intake of the turbine rises as well as, correlatively, that of the delivery of the compressor. Such a pressure increase can lead to the compressor being at its pumping limit. To limit the pressure increase, it suffices to withdraw compressed air between the outlet of the compressor and the combustion chamber. As to the variation of climatic conditions, temperature is the primary parameter. The higher the temperature, the less the capacity of the compressor. Conversely, the lower the temperature, the more the capacity of the compressor rises to the point of being able if desired to surpass the capacity of the turbine to accept a corresponding flow of fumes. It is thus frequent that the conditions of use of a same gas turbine group will be limited in winter by the turbine and in summer by the compressor. When analyzing these phenomena, the applicant has discovered that it was possible to reestablish equilibrium between the turbine and the compressor by withdrawing air at the outlet of the compressor in the case in which the operation of the group is limited by the turbine, or by injecting a supplemental flow of gas into the combustion line in the case in which the operation of the group is limited by the compressor, which thus permits compensating the disequilibra between these two elements, resulting either in the conception of these latter, or in the variations of fuel, or in each case, variations of climatic conditions, and thus to use the turbine at its maximum power.